The inventions described in the afore-mentioned related applications relate to self-propelled vehicles used primarily to transport long loads, such as whole trees or tree trunks across roadless terrain. More specifically, such prior applications relates, as does this application, to rubber tired vehicles that have wheel suspension mechanisms which provide balanced weight between its wheels and additionally permits adjustment of the steady state position of the main bed frame of the vehicle relative to a longitudinal roll axis to permit compensation for the vehicle position when operating continuously on the side of a hill, and also to facilitate unloading of the vehicle by a side dumping action in either direction.
In summary, such vehicle comprises an elongated bed frame that forms the backbone of the vehicle. This frame is balanced on modular front and rear wheel assemblies, preferably each having four quadrilaterally spaced wheels mounting massive pneumatic tires. The quad wheel suspension system is designed to provide a freedom of movement of each wheel about mutually perpendicular roll and pitch axes that are vertically spaced one above the other. The quad wheel assemblies are pivotally mounted on the bed frame so as to be moved about a roll axis which is parallel to and beneath the longitudinal axis of the main frame element. On the lower or pitch axis of each quad wheel assembly, two laterally spaced walking beam members, each carrying a pair of steerable wheels, are rockably mounted in a balanced relationship. Thus, the walking beams may rock about the pitch axis of the quad wheel assembly while the quad wheel assembly itself may pivot about the roll axis. A mechanical interconnection of the quad wheel assemblies comprises a pair of tubular torque transmission members that extend from one quad wheel assembly toward the other and are interconnected by a novel linkage system which continuously adjusts the position of the longitudinal bed frame about the roll axis to lie intermediate the positions of the quad wheel assemblies. Additionally, the linkage incorporates two power extensible links by which the steady state position of the longitudinal bed frame member relative to the roll axis may be selectively determined by the operator.
In accordance with the invention specifically disclosed and claimed in my U.S. Pat. No. 4,205,730 a unique mounting of each wheel with respect to the walking beam member permits a driving motor and brake to be incorporated in the wheel mounting mechanism for imparting required rotational movements to the wheel and, additionally, an electrical or hydraulic actuator is also incorporated in the mounting to impart individually controlled steering movements to the particular wheel. As described and claimed in my aforementioned co-pending application, Ser. No. 934,457, sensors are provided which generate signals respectively proportional to the rotational velocity of the wheel and to the angle of turn of the particular wheel. These sensor signals are inputted to a microprocessor and are compared with the turning position and rotational velocity of the wheel required to effect a particular attitude and movement of the vehicle, and compensating signals are then fed to the driving motor for the wheel and the turning actuator to cause the wheel velocity and wheel position to correspond to that required to effect a desired attitude of the vehicle.
A vehicle equipped with this combination of features has numerous advantages over prior art off-road vehicles. The individual control of the velocity and the turning angle of each wheel permits the vehicle to be manipulated through any selected one of a plurality of unusual movements or attitudes, some of which are incapable of accomplishment by any vehicle equipped with conventional driving and steering mechanisms. Any vehicle as heretofore described requires an operator's cab which is preferably in an elevated position relative to the terrain being transversed, and a power source such as a gasoline or diesel engine driving a hydraulic pump, or, if electric propulsion and steering control is to be employed, an electrical generator of sufficient capacity to provide the required traction and steering power. Hence, the operator's cab and the power unit are relatively massive in size and become a factor in the overall design of the vehicle in order to keep such units from interfering with the load carrying capability of the vehicle and at the same time, to prevent the operator's cab portion or the power unit portion of the vehicle from engaging obstacles on the ground or overhead and interfering with the mobility of the vehicle.
When the vehicle of the type heretofore described is to be employed for harvesting trees, it is quite efficient to provide a tree severing and handling means on the vehicle, which is then driven to the vicinity of the tree to be harvested, the tree engaged by a suitable clamping mechanism carried on the end of a boom, severed by a hydraulically actuated shear, and then the whole tree moved by the clamping mechanism and boom to a position lying within cradles provided on the elongated frame element of the vehicle. Such tree handling elements must, however, be disposed on the vehicle in such fashion as to not interfere with either the load carrying ability or the mobility over the rough terrain where such vehicles are to be employed.
Similarly, if the vehicle to be employed for loading and transporting of massive objects, such as large disabled vehicles or pieces of military equipment, the crane for picking up such items may be mounted on the operator's platform and conveniently controlled by the operator from the platform. For such applications, of course, the vehicle will be provided with an appropriate body or platform on the main frame element capable of receiving or supporting the massive objects to be loaded thereon.
Lastly, it is desirable that the operator's cab be capable of adjustment about a horizontal axis so that the operator is in a substantially upright position, particularly when severing and loading trees, or loading other objects.
A large number of vehicles have heretofore been proposed to be employed in the direct harvesting of trees. If a whole tree, or the whole trunk thereof, is to be bodily removed from a forest, the vehicle to transport such whole trees or trunks necessarily has to have considerable length. Prior art vehicles employed for such purpose have generally resorted to an articulated structure employing a prime mover and one or more trailers pivotally connected to the prime mover. These vehicles could obviously only be loaded with a whole tree when all of the trailed units were in substantial longitudinal alignment, and severe binding, resulting in actual breakage of the tree, would occur whenever the vehicle was steered through any reasonable degree of turn in travelling from the harvesting site to a processing station. The long rigid load represented by a bundle of whole trees superimposed on the structure effectively prevented any relative horizontal pivotal movement of the articulated trailer units and, as a result, the vehicle either became hung-up on obstructions around which the vehicle could not be steered or, portions of the tree load were broken by the forced turning movements of the articulated trailer unit. Backing of the vehicle was also very difficult.
Additionally, such prior art units suffered from the fact that the operator's control cab was generally in a fixed vertical position with respect to the vehicle. If this position were high, then the operator had to be continuously on the alert to steer around trees which were to be left standing or overhanging rock formations. If the operator's cab were left in a lowered position, it would tend to hang-up on obstructions on the ground as the vehicle traversed the uneven rugged terrain that is associated with tree harvesting operations. Similar problems were encounteded with the power unit for such vehicles, which necessarily is relatively massive in size and has to be located on the vehicle so that it does not interfere with the load carrying capacity of the vehicle nor permit the power unit to be impacted by upstanding ridges or rocks on the terrain over which the vehicle is traversed. If the vehicle was cross-wise on a slope, the operator's cab would be tilted, to the discomfort and inconvenience of the operator.
Lastly, since wheel assembly reliability is important, wheel station redundancy is advantageous. For example, massive pneumatic tires are employed on the vehicle and must necessarily be inflated to provide for movement of the vehicle across roadless terrain without damage to such tires. Thus, it becomes very desirable to provide a self jacking mechanism on the vehicle, which may be utilized in the event that any one of the pneumatic tires looses its air pressure, to effect the lifting of the particular wheel carrying the flat tire to an elevated position so that the vehicle may be moved on the remaining wheels to a repair station, hence eliminating any necessity for removing or repairing the massive pneumatic tires in the field.